File interlock

ABSTRACT

A file device includes a plurality of vertically stacked drawers or shelves provided with a safety interlock system precluding the opening of more than one storage element at a time. The cabinet contains a plurality of vertically aligned lock bars supporting rotary cam members adapted to be arcuately displaced upon movement of one storage element whereby all remaining lock bars and cam members are immobilized against vertical and rotary displacement respectively, to block movement of any additional storage element.

United States Goulish et al.

[451 Aug.-19, 1975 FILE INTERLOCK Inventors: Gabriel J. Goulish; Leo Terlecki;

Alan R. Wright, all of Youngstown, Ohio Assignee: GlF Business Equipment, lnc., Youngstown, Ohio Filed: June 28, 1974 Appl. No.: 484,250

[52] US. Cl. 312/217 [51] Int. Cl. E05B 65/46 [58] Field of Search 3l2/2l622l [56] References Cited UNITED STATES PATENTS 3;l99,937 8/1965 Mitchell 312/221 3,622,216 11/1971 Haunost ..3l2/2l9 Primary Examiner-Richard E. Moore Attorney, Agent, or FirmEmory L. Groff, Jr.

[57] ABSTRACT 15 Claims, 7 Drawing Figures FILE INTERLOCK This invention relates generally to storage or file de' vices and more particularly to an improved interlock system for precluding the operation of more than one storage element at a time within a cabinet or housing containing a plurality of storage elements.

The objectives of a file interlock system are well known to those skilled in the art to which the present invention pertains. In any storage device containing a plurality of vertically stacked storage elements such as drawers or shelves adapted to be selectively rectilinearly displaced to gain access thereto. an inherent hazard is the possibility of tipping over the storage cabinet or housing when more than one heavily loaded drawer or shelf is withdrawn at the same time. Thus the advantage of providing an interlock arrangement for precluding the operation of more than one storage element at a time will be readily apparent.

A multitude of interlock systems have been known in the past and in many of these instances extensive modification of the cabinet or housing has been necessary and/or an intricate and expensive structure was necessary in association with each one of the plurality of storage elements. Simplicity and a fool-proof operation are of paramount consideration in the construction of a file interlock as a complicated, multi-part construction can only lead to problems during operation of the device and some existing interlocks have been known to become jammed with all of the storage elements in the closed position such that it was necessary to break open the cabinet in order to release a faulty mechanism.

By the present invention an improved file interlock system is provided including a plurality of vertically aligned lock bars, all of which are freely mounted within the file cabinet for limited vertical displacement. A separate lock bar disposed adjacent each storage element carries a rotary cam member which is arcuately displaced by means of an activator or projecting means mounted upon each storage element or its suspension and which serves to rotate the cam member during operation of the storage element in order to vertically displace the respective lock bar and all other adjacent lock bars thereabove whereupon blocking means are placed in the path of each of the remaining activators in the file cabinet to preclude withdrawal of same and thus opening of any additional storage elements.

Accordingly, one of the primary objects of the present invention is to provide an improved file interlock including a plurality of vertically aligned lock bars supported by a cabinet housing and each provided with a cam member engageable by an activator mounted on each storage element and wherein the first opened storage element vertically displaces at least one lock bar and cam member to immobilize all remaining lock bars and prevent by-passing of the remaining activators.

A further object of the present invention is to provide an improved file interlock including a lock bar associated with each one of a plurality of movable storage elements and containing a rotary cam member having both greater and lesser diameter portions with projecting means carried by each storage element to rotate the lesser diameter portion with a concurrent arcuate displacement of the greater diameter portion to vertically displace the lock bar and preclude the operation of any additional storage element.

Lil

Still another object of the present invention is to provide an improved file interlock including a vertically displaceable rotary cam member mounted on a lock bar and having a lesser diameter portion engageable by an activator carried by a storage element engageable with the cam member to rotate same upon opening or closing of the storage element and wherein the activator includes an inclined surface producing a concurrent vertical displacement of the lock bar.

With these and other objects in view which will more readily appear as the nature of the invention is better understood, the invention consists of the construction, combination and arrangement of parts hereinafter more fully described, illustrated and claimed.

A practical embodiment of the present invention is shown in the accompanying drawings in which:

FIG. 1 is a perspective view, with portions broken away, of a file device provided with the interlock system of the present invention.

FIG. 2 is an enlarged side elevation of the file interlock of the present invention. and discloses the components as they would appear when the uppermost storage element is opened or withdrawn from the cabinet.

FIG. 3 is a side elevation of one of the storage element activators and rotary cam members following partial vertical displacement of the associated lock bar and rotary displacement of the cam member.

FIG. 4 is an end elevation, partly in section, taken along the line 4-4 of FIG. 3.

FIG. 5 is a composite view illustrating the sequential movement of the rotary cam member and lock bar as an activator is moved past same.

FIG. 6 is an enlarged end elevation, in section, taken on the line 66 of FIG. 2.

FIG. 7 is a fragmentary perspective view illustrating the relationship between two adjacent lock bars as they would appear when located above a storage element which has been opened, thus blocking passage of the activator shown.

Similar reference characters designate corresponding parts throughout the several figures of the drawings.

Referring now to the drawings, particularly FIG. 1, the present invention will be understood to comprise an improved interlock system for use in a storage device containing a plurality of movable storage elements in order to preclude the operation or withdrawal of more than one of the storage elements at any one time. The invention is illustrated in association with a file F of the type including a cabinet or housing C having a plurality of vertically stacked storage elements or drawers D. It will be understood that the structure of the subject interlock may be just as readily incorporated in combination with other forms of storage devices such as the currently popular lateral files or any device containing a plurality of vertically stacked elements adapted to be selectively moved in a rectilinear manner from a stor age to an access position.

Generally described, the present interlock includes a plurality of lock bars L1L5 mounted within the cabinet C for vertical sliding displacement juxtaposed the sides 1 of the storage elements or drawers D. When all of the drawers are closed the lock bars Ll-LS all rest upon one another and the cabinet bottom by gravity and upon the opening or withdrawal of any one of the drawers D, actuating or projecting means in the form of an activator 2 carried by each drawer, cooperates with a cam member mounted upon the adjacent lock bar to vertically displace all lock bars above the level of the opened drawer whereupon all such elevated lock bars block any subsequent attempt to withdraw their associated drawers and at the same time all lock bars beneath the opened drawer are immobilized to block any attempt to open their associated drawers.

The plurality of lock bars L1L5 may be suitably mounted within the confines of the cavity 4 defined by the cabinet C by any suitable means permitting of their free vertical sliding displacement. FIG. 2 of the drawings illustrates most clearly a simple, positive mounting means for the lock bars comprising a rear upright or framing member 5 attached to the inner surface of one sidewall 6 of the tile cabinet and which contains guide means in the form of a vertical channel 7 extending the full height of the upright 5 to provide an unobstructed guide means extending from the top wall 8 of the cabinet to the bottom wall 9 thereof. Each lock bar contains a main body section comprising the majority of the length thereof, and with the exception of the uppermost lock bar Ll, terminates at its uppermost portion with an in-turned flange tip 11. As shown in FIG. 6, each lock bar with the exception of the lowermost lock bar L5, is provided with an offset bottom tip 12 disposed in a plane located immediately to the rear of the ,main body section of each lock bar.

The relative vertical position of any one of the lock bars is controlled upon actuation of the rotary cam member 3 which is freely mounted for limited arcuate displacement upon the lower portion of lock bars LI-L4 by means of the rivet 13. Each of the cam members 3 will be understood to comprise a central main body 14 having an annular cam periphery 15 defining a lesser diameter portion thereof. The rear face 16 of each cam member is juxtaposed the supporting lock bar and extends radially to provide a radial cam flange 17 having an arcuate periphery 18 describing a circum ference of greater than 180. As will appear more clearly later on in the description, only a small portion of the arcuate periphery 18 is utilized during operation of the subject interlock, while the segment 19 as shown in FIG. 5 serves primarily as a counter-weight to neutralize the mass of the peripheral portion 18 so that the cam member will not rotate on its own due to gravity. The rotary displacement of the rotary cam member 3 is limited by means of an arcuate slot 20 formed in the radial cam flange 17 immediately adjacent the main body portion 14 thereof and which cooperates with the limit pin 21 carried by the main body section 10 of the lock bar such that the normal position of the cam member is as shown in FIG. 7 while the alternate position of the cam member is shown most clearly in FIG. 3 of the drawings.

The above reference to alternate positioning of the rotary cam members 3 will be understood to cause alteration of the overall effective height of the vertically aligned lock bars LIL5 contained within the guide means or vertical channel 7. When all of the drawers or storage elements are closed within the cabinet C all of the rotary cam members 3 are in the position as illus trated by the two lowermost cam members of FIG. 2 such that the lesser diameter portion of each of the cam members is located immediately juxtaposed the inturned flange tip 11 of the next lower lock bar as shown most clearly in the lower portion of FIG. 6 of the drawings. At this stage the lock bars may be considered to be collapsed and the effective overall height of the plurality of lock bars is at its minimum with the top offset tip 22 of the uppermost lock bar Ll being located at the dotted line position as shown in FIG. 2 so that a free space 23 is formed between the edge of this offset tip and the top wall 8 of the cabinet C. With this structure in mind it will follow that upon the arcuate displacement of any one of the rotary cam members 3 concurrently with an elevation of the connected lock bar, the greater diameter portion of the radial cam flange 17 is moved to a 6 oclock position relative the rivet 13 and the arcuate periphery 18 will thereupon engage the upper surface of the next lower intumed flange tip 11 so that the structure will appear as in the upper portions of FIG. 6 and FIG. 2. When the elevation of any one lock bar occurs as a result of the arcuate displacement of a rotary cam member 3, the aforedescribed free space 23 will no longer exist as the top offset tip 22 of the uppermost lock bar L1 is moved to a position immediately juxtaposed the inner surface of the cabinet top wall 8. It is important to realize that this vertical displacement of the offset tip 22 and disappearance of the free space 23 will occur when any one of the rotary cam members 3 is thusly arcuately displaced and elevated. Such will always be the case since, when a lower rotary cam member is arcuately displaced and its respective lock bar is elevated it will follow that all other lock bars disposed above the elevated lock bar will be concurrently elevated a similar distance as all of the uppermost lock bars are directly bearing upon each lock bar therebeneath due to the engagement of the lesser diameter portion of the remaining cam members upon the adjacent intumed flange tip 11 of-the next lock bar and the abutment of the lock bar bottom tips 12 upon the next lower lock bar.

The projecting means causing the elevation and concurrent displacement of the rotary cam members to automatically actuate the interlock feature of the present invention will now be discussed. The activator, generally designated 2, is a rigid member carried by each of the rectilinearly displaceable drawers and is shown in the drawings as being attached to the drawer suspension, generally designated 24. Alternatively, each activator 2 may be connected directly to a drawer side 1 but a more rigid and positive connection is achieved by attaching the actuator to the drawer suspension channel 25 which may be of any suitable well known construction and cooperates with a cabinet suspension channel 26, with or without an intermediate slide chan' nel 26a.

The activator 2 comprises a saddle including a front ramp 27, horizontal top track 28 and a rear ramp 29, and is affixed to the drawer or the drawer suspension channel 25 so that when the drawer is closed the activator will be located to the rear of the lock bars and cam members as shown most clearly in the central and lower portions of FIG. 2 of the drawings. As shown in FIGS. 4, 6 and 7 the activator is mounted so that the path of its rectilinear travel passes through the lower half of the central main body 14 of the rotary cam members when these cam members are disposed in the collapsed position or wherein the lesser diameter portions thereof are located immediately above the inturned flange tips 11 of the next lower lock bar.

Several critical features are present in the construction and mounting of the components forming the activators. First, the inner edge 30 of the front ramp 27, top track 28 and rear ramp 29 is located in a plane well clear of the radial cam flange 17 of each cam member as shown most clearly in FIG. 4 and the lower portion of FIG. 6 so that during horizontaldisplacement of the activator there is no interference between the saddle components thereof and the radial cam flange of 1 the cam member. Secondly, when all of the drawers are closed and the lock bars are in their collapsed condition it is important to note that the leading edge 31 of the front ramp 27 of each activator is disposed slightly above the horizontal plane of the respective inturned flange tip 11 and at the same time is located slightly below the horizontal plane of the bottom of the central main body 14 of the respective rotary cam member 3 as shown in the central and left hand portions of FIG. 5 of the drawings. A positive minimal spacing between the bottom of the cam periphery and the top of the adjacent flange tip 11 is ensured by providing a narrow rib 15a on the main body 14, extending between the ends of the radial cam flange 17. Thus, as shown in the lower portion of FIG. 6, the rib 15a and offset bottom tip 12 combine to define a spacing S.

With the above structure in mind, it will follow that when a first drawer is withdrawn from its storage position the respective activator 2 and adjacent cam member and lock bar will undergo the displacements as shown in FIG. 5 wherein the leading edge 31 of the front ramp 27 initially enters the spacing S and passes beneath the lesser diameter portion of the cam member central main body 14 and above the flange tip 11 of the lock bar L2 without any displacement of the interlock components until the activator has been moved to the position reflected by the central portion of FIG. 5 whereupon continued horizontal displacement of the activator causes a concurrent vertical displacement or elevation of the lock bar L1 and a clockwise rotary displacement of the cam member 3 as the upper surface of the front ramp 27 engages the annular cam periphery 15 of the central main body 14 of the cam member. In order to preclude slippage between the cam periphery l5 and the front ramp 27 and also to enhance the to the position as shown in FIG. 2 the lock bar L1 is thus elevated due to the arcuate displacement of its respective cam member and radial cam flange 17 so that .all of the free space 23 has been eliminated, thereby immobilizing all remaining lock bars located beneath the elevated lock bar L1. Therefore, if one were to at will be possible since the lock bar 2 has been totally immobilized and cannot be vertically displaced. Attempts to forcefully withdraw this other drawer 'only result in quietness of operation, the central main body' 14 of the cam member may be provided with an annular friction ring 32 of rubber-like composition and which slightly extends beyond the circumference of the cam periphery 15. The inclination of the front ramp 27 of the activator and the location of the leading edge 33 of the radial cam flange 17 are selected to ensure that the lock bar L1 will be initially elevated a sufficient amount to ensure that the arcuate periphery 18 of the radial cam flange 17 will be disposed above the top of the inturned flange 11 of the lock bar L2 by the time the cam member has been arcuately displaced to the position as shown in the right hand portion of FIG. 5. Continued horizontal displacement of the activatonfor example. to the position as shown in the upper portion of FIG.

2, results in the full arcuate displacement of the cam member to the limit as defined by the pin 21 with the result that the lock bar I..1 has been vertically displaced an amount calculated to move the top offset tip 22 thereof to a point immediately juxtaposed the undersurface of the cabinet top drawer 8, thereby eliminating all significant free space 23 within the vertical channel or guide means 7 to immobilize all of the lock bars.

The interlock feature of the present invention may now be readily understood by a review of FIGS. 2 and 6 of the drawings. With the uppermost drawer and its respective activator having been horizontally displaced a further urging of the top offset tip 22 into tighter engagement with the undersurface of the cabinet top wall 8. A slight space will still be seen betweenthe top of the offset tip 22 and the undersurface of the cabinet top wall 8 in FIG. 2; however, this is provided solely to preclude any binding of the lock bars when the first drawer I is removed and is not enough space to permit the opening of any second drawer as it will be realized that, before an activator may pass beneath a cam member, there must be available a free space 23 of a dimension no less than the dimension between an activator bottom plate 34 and top track 28, a distance which is comparable to the difference between the radius of the rib 15a and periphery 18 of each cam member.

FIGS. 2 and 6 illustrate the'interlock structure as it appears when the uppermost one of the lock bars Ll has been vertically displaced due to the opening of the top one of a plurality of drawers in a file cabinet. When a second one or lower drawer is the first one to be opened there is no change in'the relationship between the lower ones of the lock'barssince they still remain in their normal collapsed position, such as the lock bars L2-L5 of FIG. 2. However, the lock bar next above that which is directly vertically displaced upon the withdrawal of a drawer would then appear as shown in FIG. 7 of the drawings. Assuming that the second drawer has been withdrawn and the rotary cam mem ber 3 attached to lock bar L2 has been arcuately displaced together with the elevation of lock bar L2, it will be understood that the inturned flange tip of lock bar L2 has concurrently likewise elevated lock bar L1 to eliminate the'free space 23-at the top of the vertical channel 7. The arrangement of the interlock structure as it pertains to the closed drawer above the one which has been opened is slightly different than that for all the drawers located below the one which has been opened. As shown in FIG. 7, if the top closed drawer is attempted to be opened, the front ramp 27 of the activator will not strike the rotary cam member at all, but instead, since the inturned flange tip 11 of the lock bar L2 has been elevated, the leading edge 33 of this activator will be disposed below the horizontal plane of this inturned flange tip and thus the central portion of the front ramp 27 will strike the rear edge of the flange tip, thereby blocking any further [horizontal displacement of the activator and its associated drawer.

The sequence of movement of the interlock components is just reversed during closing of an opened drawer. The rear ramp 29 of the activator saddle engages the angular cam periphery 15 of the cam member main body 14 immediately adjacent the rear of the top track 28 to arcuately displace the radial cam flange 17 thereof in a counter-clockwise direction as the bottom plate 34 passes over the flange tip 11 thereby removing the arcuate periphery 18 from its position overlying the adjacent inturned flange tip 11 so that when the activator has been moved entirely rear of the rotary cam member the associated lock bar has dropped by gravity to its normal position wherein the lesser diameter portion of the rotary cam member is disposed immediately above the flange tip of the next lower lock bar with the rib a resting upon the tip 11 and the free space 23 is again present.

We claim:

1. A file cabinet having a plurality of vertically stacked storage elements provided with interlock means for preventing the opening of more than one said element at a time, said interlock means including, a plurality of vertically aligned lock bars in said cabinet for limited vertical displacement therein, guide means in said cabinet containing said lock bars and defining the limit of vertical displacement of said lock bars, cam means carried by each said lock bar each having rotatable lesser and greater diameter portions, said lesser diameter portions normally disposed immediately adjacent the next lower one of said lock bars, means mounting each said storage element within said cabinet for substantially horizontal rectilinear movement therein, activator means horizontally movable concurrently with each said storage element to engage one said cam means to vertically displace its respective lock bar and concurrently rotate said cam means whereby, when one said cam means has been rotated by said activator means and its respective lock bar elevated thereby, all remaining said lock bars and cam members are immobilized and block movement of any additional activator means and associated storage elements therepast.

2. A file cabinet according to claim 1 wherein, said cabinet includes a sidewall and said lock bar guide means comprise a vertical channel provided adjacent the interior of said side wall.

3. A file cabinet according to claim 1 wherein, said cam means comprise a rotary cam member, said lesser diameter portion including a central main body having an annular periphery, and said greater diameter portion includes a radial cam flange having an arcuate periphery.

4. A file cabinet according to claim 1 wherein, said mounting means include at least a pair of suspension channels between each side of each said storage elements and the sides of said cabinet.

5. A file cabinet according to claim 1 wherein, said activator means include a front ramp engageable with said cam means lesser diameter portion to rotate said greater diameter portion as said storage element is horizontally displaced.

6. A file cabinet according to claim 1 wherein, at least one said lock bar includes an inturned flange tip at its top and said cam means carried by the next higher of said lock bars rests upon said flange tip.

7. A file cabinet according to claim 2 wherein, said lock bars normally are disposed one upon another when all said storage elements are in the closed position within said cabinet to provide a free space between the top of the uppermost of said lock bars and the upper limit of said channel whereby, opening of one said storage element horizontally displaces its associated activator to engage said cam means lesser diameter portion and elevate the attached lock bar and any higher lock bar so that said free space is occupied by the top of the uppermost one of said lock bars, and said concurrent rotation of said cam means arcuately displaces said greater diameter portion to a position below said lesser diameter portion and overlying the top of the most lower one of said lock bars.

8. A file cabinet according to claim 3 wherein, said annular periphery is provided with friction means enhancing positive engagement with said activator.

9. A file cabinet according to claim 3 wherein, said rotary cam member includes a rib radially extending from said main body adjacent to and in the vertical plane of said radial cam flange whereby, said rib normally supports its associated lock bar upon the top of the next lower one of said lock bars when the adjacent one of said storage elements is in the closed position.

10. A file cabinet according to claim 4 including, one of each said pairs of channels fixed to each side of said storage element and said activator means are fixed to one said storage element affixed channel at a point located to the rear of said lock bars when said storage element is in the closed position.

11. A file cabinet according to claim 5 wherein, the height of said ramp is no less than the difference in the radius of said lesser and greater diameter portions of said cam means.

12. A file cabinet according to claim 5 wherein, said ramp includes a leading edge disposed below said cam means lesser diameter portion and above the top of the next lower one of said lock bars.

13. A file cabinet according to claim 5 wherein, said activator includes a central top track and a rear ramp.

14. A file cabinet according to claim 6 including, rib means on said cam means engageable with said lock bar flange tip to provide a minimal spacing between said lesser diameter portion and said flange tip through which said activator passes when the adjacent said storage element is opened.

15. A file cabinet according to claim 7 wherein, said activator includes a front ramp and the height of said channel free space when all said storage elements are closed is substantially less than twice the height of said ramp whereby only one said cam means may be vertically displaced at a time. 

1. A file cabinet having a plurality of vertically stacked storage elements provided with interlock means for preventing the opening of more than one said element at a time, said interlock means including, a plurality of vertically aligned lock bars in said cabinet for limited vertical displacement therein, guide means in said cabinet containing said lock bars and defining the limit of vertical displacement of said lock bars, cam means carried by each said lock bar each having rotatable lesser and greater diameter portions, said lesser diameter portions normally disposed immediately adjacent the next lower one of said lock bars, means mounting each said storage element within said cabinet for substantially horizontal rectilinear movement therein, activator means horizontally movable concurrently with each said storage element to engage one said cam means to vertically displace its respective lock bar and concurrently rotate said cam means whereby, when one said cam means has been rotated by said activator means and its respective lock bar elevated thereby, all remaining said lock bars and cam members are immobilized and block movement of any additional activator means and associated storage elements therepast.
 2. A file Cabinet according to claim 1 wherein, said cabinet includes a sidewall and said lock bar guide means comprise a vertical channel provided adjacent the interior of said side wall.
 3. A file cabinet according to claim 1 wherein, said cam means comprise a rotary cam member, said lesser diameter portion including a central main body having an annular periphery, and said greater diameter portion includes a radial cam flange having an arcuate periphery.
 4. A file cabinet according to claim 1 wherein, said mounting means include at least a pair of suspension channels between each side of each said storage elements and the sides of said cabinet.
 5. A file cabinet according to claim 1 wherein, said activator means include a front ramp engageable with said cam means'' lesser diameter portion to rotate said greater diameter portion as said storage element is horizontally displaced.
 6. A file cabinet according to claim 1 wherein, at least one said lock bar includes an inturned flange tip at its top and said cam means carried by the next higher of said lock bars rests upon said flange tip.
 7. A file cabinet according to claim 2 wherein, said lock bars normally are disposed one upon another when all said storage elements are in the closed position within said cabinet to provide a free space between the top of the uppermost of said lock bars and the upper limit of said channel whereby, opening of one said storage element horizontally displaces its associated activator to engage said cam means'' lesser diameter portion and elevate the attached lock bar and any higher lock bar so that said free space is occupied by the top of the uppermost one of said lock bars, and said concurrent rotation of said cam means arcuately displaces said greater diameter portion to a position below said lesser diameter portion and overlying the top of the most lower one of said lock bars.
 8. A file cabinet according to claim 3 wherein, said annular periphery is provided with friction means enhancing positive engagement with said activator.
 9. A file cabinet according to claim 3 wherein, said rotary cam member includes a rib radially extending from said main body adjacent to and in the vertical plane of said radial cam flange whereby, said rib normally supports its associated lock bar upon the top of the next lower one of said lock bars when the adjacent one of said storage elements is in the closed position.
 10. A file cabinet according to claim 4 including, one of each said pairs of channels fixed to each side of said storage element and said activator means are fixed to one said storage element affixed channel at a point located to the rear of said lock bars when said storage element is in the closed position.
 11. A file cabinet according to claim 5 wherein, the height of said ramp is no less than the difference in the radius of said lesser and greater diameter portions of said cam means.
 12. A file cabinet according to claim 5 wherein, said ramp includes a leading edge disposed below said cam means'' lesser diameter portion and above the top of the next lower one of said lock bars.
 13. A file cabinet according to claim 5 wherein, said activator includes a central top track and a rear ramp.
 14. A file cabinet according to claim 6 including, rib means on said cam means engageable with said lock bar flange tip to provide a minimal spacing between said lesser diameter portion and said flange tip through which said activator passes when the adjacent said storage element is opened.
 15. A file cabinet according to claim 7 wherein, said activator includes a front ramp and the height of said channel free space when all said storage elements are closed is substantially less than twice the height of said ramp whereby only one said cam means may be vertically displaced at a time. 